eaw@Alliant.COM (Eric Woudenberg) (11/11/89)
I have a MacPlus that at one time had a capacitor on it's video board go bad. I've replaced the capacitor and things have been working fine for at least a year. I noticed soon after I had repaired it that the video was slightly trapezoidal, with the left edge of the screen being smaller than the right edge. I looked at my Father's machine (which has also had a video failure and repair) and noticed that his was also trapezoidal, only with the left edge bigger than the right. Has anyone seen this? Is there an adjustment/replacement which I can make to fix it? Thanks, Eric Woudenberg
user7@amdcad.AMD.COM (Unix class) (11/18/89)
In article <3525@alliant.Alliant.COM> eaw@alliant.Alliant.COM (Eric Woudenberg) writes: >I have a MacPlus that at one time had a capacitor on it's video board >go bad. I've replaced the capacitor and things have been working fine >for at least a year. I noticed soon after I had repaired it that the >video was slightly trapezoidal, with the left edge of the screen being >smaller than the right edge. I looked at my Father's machine (which >has also had a video failure and repair) and noticed that his was also >trapezoidal, only with the left edge bigger than the right. > I'll make a guess and say that it sounds like as if the capacitor is not the proper value. You can check this by adding another capacitor of the same type and similar value(try 50% of the other) in parallel. If this makes it more rectangular, then you can add an appropriate value of a capacitor in parallel without taking out the other one. But if it made the screen more trapezoidal then you'll have to take out the capacitor and replace it with one of smaller value. If something else happens entirely, then the reason is (prbably?) something else. If it fries your computer, well ... uhh.. :-) But that shouldn't happen. I'd risk trying this if this happened to me. - Chung
steveg@umd5.umd.edu (Steve Bruce Green) (11/18/89)
In article <28092@amdcad.AMD.COM: user7@amdcad.UUCP (Unix class) writes: :In article <3525@alliant.Alliant.COM: eaw@alliant.Alliant.COM (Eric Woudenberg) writes: ::I have a MacPlus that at one time had a capacitor on it's video board ::go bad. I've replaced the capacitor and things have been working fine ::for at least a year. I noticed soon after I had repaired it that the ::video was slightly trapezoidal, with the left edge of the screen being ::smaller than the right edge. I looked at my Father's machine (which ::has also had a video failure and repair) and noticed that his was also ::trapezoidal, only with the left edge bigger than the right. :: : :I'll make a guess and say that it sounds like as if the capacitor is not :the proper value. You can check this by adding another capacitor of the :same type and similar value(try 50% of the other) in parallel. : If this makes it more :rectangular, then you can add an appropriate value of a capacitor in :parallel without taking out the other one. But if it made the screen more :trapezoidal then you'll have to take out the capacitor and replace it :with one of smaller value. If something else happens entirely, then :the reason is (prbably?) something else. If it fries your computer, well :... uhh.. :-) But that shouldn't happen. I'd risk trying this if :this happened to me. If you look at the yolk of the crt, you will see a bunch of small magnets around the outter side of the it. If you turn thses magnets you can distort the picture in the way you described. Sounds like you may have turned on em when you repaired the power board. If not, go ahead and turn the on in the distorted corner too see if that can fix it. Be careful, it is real easy to mess up the picture. You cant cause any damage but its a pain to fix. Also, make sure the cap you replaced what the correct value. The capacitor value should be 3.9uf NON-POLOR. I have seen larger vlaues work ok and not disort the picture in this way but in other ways. -S